To answer this question, let's review each of the given options:
Option A) Color skyColor = BLUE;
This option assigns the enum constant "BLUE" to the variable "skyColor". This is incorrect because "BLUE" is a member of the "Color" enum and should be accessed as "Color.BLUE".
Option B) Color treeColor = Color.GREEN;
This option correctly assigns the enum constant "GREEN" from the "Color" enum to the variable "treeColor". This is a valid way to access enum constants.
Option C) Color purple = new Color(0xff00ff);
This option attempts to create a new enum constant using the constructor of the "Color" enum. However, enum constants are predefined and cannot be created using the constructor. This is incorrect.
Option D) if (RED.getRGB() < BLUE.getRGB()) {}
This option correctly accesses the "getRGB()" method of the "RED" and "BLUE" enum constants and performs a comparison. This is a valid way to access enum constants and their methods.
Option E) Color purple = Color.BLUE + Color.RED;
This option attempts to add the enum constants "BLUE" and "RED". However, enum constants cannot be added together using the "+" operator. This is incorrect.
Option F) if (Color.RED.ordinal() < Color.BLUE.ordinal()) {}
This option correctly accesses the "ordinal()" method of the "RED" and "BLUE" enum constants and performs a comparison. This is a valid way to access enum constants and their methods.
Therefore, the correct options are B) Color treeColor = Color.GREEN; and F) if (Color.RED.ordinal() < Color.BLUE.ordinal()).